| 摘要 |
1,123,418. Etching. FARBWERKE HOECHST A.G. 23 Nov., 1965 [12 Dec., 1964], No. 49678/65. Heading B6J. A polyoxymethylene printing block is prepared by an etching process in which there is applied to the portion of the block to be etched, at a temperature between 40‹ C. and the softening point of the polyoxymethylene, an etching agent comprising an acid or a compound which reacts to form an acid at a temperature above 40‹ C., thickened by an acid-proof filler to yield a paste. The acid may be phosphonic or sulphosalicylic and the compound which reacts to form an acid may be an ammonium salt of a castor oil sulphuric acid ester (Turkey red oil). The filler may be titanium dioxide, barium sulphate, chromium-III-oxide or pyrogenically prepared silicon dioxide. A wetting agent e.g. the reaction products of tributyl phenol and ethylene oxide may be present in the etching agent. |
